aust mutants exhibit defects in chromosome segregation and cytokinesis. (A and C) Wild-type onion stage spermatids contain a single phase-light nucleus and phase-dense Nebenkern of similar size. (B) aust spermatids contain a single, large Nebenkern surrounded by multiple nuclei of varying sizes. (D–J) Examples of spermatids seen in aust mutants (Table I). (K and L) Phase contrast images of wild-type (K) and aust mutant (L) spermatocytes in telophase I. Wild-type cells possess a robust central spindle that is constricted at the site of cytokinesis (arrows). In contrast, aust mutant cells show no central spindle (arrows). Bars, 20 μm.